(1) Field of the Invention
This invention relates to an actuator which applies driving force to a driven member. More particularly, the present invention relates to an actuator which uses a piezo-electric device exhibiting a piezo-electric effect and applies driving force to a driven member.
(2) Description of the Prior Art
Actuators for applying driving force to a driven member are generally classified into the electric input type and the fluid input type. The former actuators are typified by electric motors while the latter actuators are typified by oil-pneumatic motors, oil-pneumatic cylinders and the like.
With the development of piezo-electric devices in recent years, various actuators using piezo-electric devices have been proposed. An example of such an actuator using piezo-electric devices is described on pages 470 to 473 in the chapter "Piezokeramische Vibromotoren" of the literature entitled "FEINGERATE-TECHNIK" published in October, 1983 in East Germany. This prior art reference discloses an actuator using piezo-electric devices in which the tips of two piezo-electric devices, that are disposed diagonally in such a manner as to cross each other, are connected by a coupling element in a triangular form in such a fashion that the vibration of each piezo-electric device makes the coupling element cause circular or elliptic motion, and this coupling element causing such a motion is brought into contact with a driven member so as to actuate the same.
In the actuator of the kind described above, the driven member is actuated by the coupling element causing a motion with a circular orbit that is obtained by the synthesis of the vibration displacement of alternate elongation and contraction of each piezo-electric device, and brought into contact with the driven member. In this instance, each piezo-electric device must undergo bending deformation; hence it must be thin. Therefore, each piezo-electric device is likely to suffer deformation such as buckling, and the driving force of each piezo-electric device is small so that the driving force applied to the driven member is also small. As a result, a large driving force can not be applied to the driven member.